1. Field of Invention
This invention relates to instant photography and, more particularly, it concerns an instant photography system in which a novel self-developing film unit of the integral type is processed after exposure by direct passage of the exposed unit through a pressure nip provided by processing apparatus designed to accommodate the structure of the film unit.
2. Description of the Prior Art
In the art relating to self-developing film units of the type used in instant cameras, the term "integral" is commonly used to describe self-developing film units in which all components originally constituting the unit remain as a part thereof during exposure, processing, and in the ultimate photograph. Such film units are thus distinguished from those self-developing film units in which part of the original unit is removed from the physical structure of the unit between exposure and attainment of the final photograph. The term "integral," therefore, as used herein and in the appended claims, is intended to identify self-developing film units of the type in which all original parts of the unit remain in the photograph as distinguished from common usage of the term to suggest a one-part structure.
Integral self-developing film units are well known in the art and exemplified by the disclosures of the following U.S. patents among others: U.S. Pat. Nos. 3,621,768; 3,761,268; 3,816,128; 4,092,167; 4,247,626; and 4,356,248. Such film units typically include a pair of superposed rectangular sheets, at least one of which is transparent, retained by a frame-like binder having leading and trailing edges joined by side edges. The frame margin at the leading edge is relatively wide to accommodate a rupturable pod of processing fluid to be spread between the two sheets upon passage of the film unit through a pressure nip, usually defined by a pair of rollers. Chemicals contained between the two sheets respond to light during exposure and to the processing fluid after exposure to provide a photographic image visible through the transparent sheet or sheets of the framed unit.
In addition to the aforementioned components which are apparent from observation of the film unit exterior, such units contain interior structural components which heretofore have been important to the diffusion transfer developing process initiated by spread of the pod-contained processing fluid into contact with the chemicals contained between the two superposed sheets of the unit. In this context, for example, it is important that the thickness of the processing fluid layer spread throughout the area of the superposed sheets be uniform and controlled within extremely close tolerances on the order of 0.0001 inch. The thickness of the processing fluid layer will, moreover, vary by such tolerance depending on the sensitometry of a given batch of chemicals used in the film units. Heretofore, the thickness of the processing fluid layer spread between the superposed sheets by pressure rollers, for example, has been controlled by introducing a pair of rails between the superposed sheets and extending along the marginal side edges thereof between the leading and trailing edges of the film unit. In this way, the precise thickness of the rails and thus the precise thickness of the processing fluid layer could be controlled within the indicated tolerances.
Another interior adjunct of integral self-developing film units heretofore used has involved the requirement for a trap at the trailing edge of the unit to accommodate any excess of processing fluid remaining after the spread of fluid between the superposed sheets. Such traps have typically employed a separate spacer provided with fluid receiving pockets or the like, the spacers assuring retention of the excess processing fluid within the unit upon passage through the pinch roller pair. A review of the above cited patents will reveal other film unit structural refinements resulting from the extensive developmental effort which is contributed to the success of such units.
While the construction of integral self-developing film units presently in use has been highly effective in the attainment of high-quality photographic prints and photographic transparencies, there is a need for reduced structural complexity in film units of this type and a corresponding reduction in manufacturing costs.